This program will use a systems biology approach to investigate the mechanism(s) whereby human melanocytes undergo neoplastic transformation, clonal expansion, and malignant progression to cutaneous melanomas. The proposed studies are based on the premise that an environmental carcinogen, solar radiation, contributes to development of melanoma by inducing chromosomal damage in proliferating melanocytes. Malignant melanomas are of significant public health concern because their incidence is rising and no effective medical intervention is available for reducing morbidity and mortality. The guiding hypothesis of this program is that breakdowns in the systems of defense against DNA damage underlie the acquisition by meianocytes of a mutator phenotype, which reduces the effective dose of solar radiation needed to induce each subsequent step in the multi-stage development of cancer. Functional defects in DNA repair and cell cycle checkpoints, individually and in concert, contribute to genome destabilization, and thus increase the probability of accumulation in a single clone of the genetic alterations required for development of melanoma. Three research projects and three service cores will interact extensively to monitor quantitatively and qualitatively the system of response to DNA damage in UV-damaged human and murine melanocytes. Two research projects will determine how nucleotide excision repair, post-replication repair, double-strand break repair, and cell cycle checkpoint responses to UV-induced DNA damage cooperate to suppress chromosomal aberrations and allelic deletions in the melanoma tumor suppressor locus CDKN2A/INK4A. Functional assays will associate chromosomal instability and defective DNA damage responses in melanoma cell lines and melanocytes with alterations in melanomagenic genes. A third research project uses in vivo models of melanoma in mice and humans to monitor chromosomal destabilization during stages of development of melanoma. Program investigations will determine how activating mutations in melanoma oncogenes and inactivating mutations in melanoma suppressor genes contribute to chromsomal instability and malignant progression. New findings will lead to the discovery of biomarkers with potential therapeutic and prognostic value for specific types of melanomas and different stages of melanoma progression. Computational models will be created to predict how DNA repair and checkpoint functions suppress UV-induced chromsomal damage. These studies will establish the degree to which melanoma-associated genetic alterations alone and in combinations contribute to a UV-chromosomalmutator phenotype and enhance environmental carcinogenesis. Lessons learned in this program will also impact on methods of risk assessment by showing that the effective dose of a carcinogen falls during the multi-step development of cancer.